Enteric coating material hypromellose acetate succinate, which may hereinafter be also called “HPMCAS”, has been widely used for the applications including a coating application, an application of controlled drug release, and an application of producing a solid dispersion containing the HPMCAS and a poorly water-soluble drug through hot melt extrusion or spray drying.
When HPMCAS is used for coating, a variety of coating methods can be applied. Examples include coating of a solution obtained by dissolving HPMCAS in an organic solvent, aqueous dispersion coating of an aqueous dispersion obtained by dispersing fine granules of HPMCAS in water in the presence of a plasticizer, alkali-neutralized aqueous coating of HPMCAS partially neutralized with an aqueous alkali solution, and dry coating in which fine particles of HPMCAS are directly applied while spraying a plasticizer.
HPMCAS is a polymer obtained by replacing the hydrogen atoms of the hydroxyl group of its glucose units forming a cellulose backbone with four kinds of substituents in total, wherein the two kinds of substituents are a methyl group (—CH3) and a hydroxypropoxy group (—C3H6OH) for ether structures and the other two kinds of substituents are an acetyl group (—COCH3) and a succinyl group (—COC2H4COOH) for ester structures (refer to a brochure by Shin-Etsu Chemical Co., Ltd. titled “Hydroxypropyl methyl cellulose acetate succinate Shin-Etsu AQOAT”.).